This invention relates generally to the field of electronic circuits. More particularly, some embodiments of the invention are directed to detection of acoustic signals in a low-power circuit configuration.
Acoustic signals, such as voice, are usually detected using microphones, which can be used in many applications such as telephones, hearing aids, public address systems for concert halls and public events, motion picture production, live and recorded audio engineering, sound recording, two-way radios, megaphones, radio and television broadcasting, and in computers for recording voice, speech recognition, VoIP, and for non-acoustic purposes such as ultrasonic sensors or knock sensors.
Several different types of microphones are in use, which employ different methods to convert the air pressure variations of a sound wave to an electrical signal. A condenser microphone uses the vibrating diaphragm as a capacitor plate. An electret microphone is a type of electrostatic capacitor-based microphone using a permanently charged material. An electret is a stable dielectric material with a permanently embedded static electric dipole moment. For example, electret microphones can use polytetrafluoroethylene (PTFE) plastic, either in film or solute form, to form the electret. An electret microphone capsule may include an electret microphone and a field effect transistor (FET), which usually needs a power supply. Conventional circuits often have separate bias circuit and a voice detection processing circuit, and the DC bias is known to consume power.
Power consumption is a great concern, as voice command applications in mobile devices are becoming more popular. Voice command processing that requires high energy can be performed in the cloud. However, the circuitry that enables the voice command processing is still implemented on the mobile devices and requires energy from the mobile device battery. The circuits that process audio signals picked up by the microphone often consumes substantial power, because these circuits are typically always running as a voice command or keyword can arrive at any time.
Therefore, for power-efficient implementation and long battery life, it is desirable to have very low power circuits that process audio signals picked up by the microphone.